Am 24.03.25 um 09:35 schrieb Tvrtko Ursulin:
>
> On 21/03/2025 15:58, Christian König wrote:
>> Sometimes drivers need to be able to submit multiple jobs which depend on
>> each other to different schedulers at the same time, but using
>> drm_sched_job_add_dependency() can't fail any more after the first job is
>> initialized.
>>
>> This function preallocate memory for dependency slots so that no ENOMEM
>> can come later while adding dependencies.
>>
>> v2: rework implementation an documentation
>>
>> Signed-off-by: Christian König <christian.koe...@amd.com>
>> ---
>> drivers/gpu/drm/scheduler/sched_main.c | 44 ++++++++++++++++++++++++--
>> include/drm/gpu_scheduler.h | 2 ++
>> 2 files changed, 43 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c
>> b/drivers/gpu/drm/scheduler/sched_main.c
>> index 4d4219fbe49d..ee3701f346b2 100644
>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>> @@ -852,6 +852,39 @@ void drm_sched_job_arm(struct drm_sched_job *job)
>> }
>> EXPORT_SYMBOL(drm_sched_job_arm);
>> +/**
>> + * drm_sched_job_prealloc_dependency_slots - avoid ENOMEM on adding
>> dependencies
>> + * @job: scheduler job where dependencies will be added
>> + * @num_deps: number of dependencies to preallocate slots for
>> + *
>> + * Sometimes drivers need to be able to submit multiple jobs which depend on
>> + * each other to different schedulers at the same time, but using
>> + * drm_sched_job_add_dependency() can't fail any more after the first job is
>> + * initialized.
>> + *
>> + * This function preallocate memory for dependency slots so that no ENOMEM
>> can
>> + * come later while adding dependencies.
>> + *
>> + * Return:
>> + * 0 on success, or an error on failing to expand the array.
>> + */
>> +int drm_sched_job_prealloc_dependency_slots(struct drm_sched_job *job,
>> + unsigned int num_deps)
>> +{
>> + u32 id = 0;
>> + int ret;
>> +
>> + while (num_deps--) {
>> + ret = xa_alloc(&job->dependencies, &id, XA_ZERO_ENTRY,
>> + xa_limit_32b, GFP_KERNEL);
>> + if (ret != 0)
>> + return ret;
>> + }
>> +
>> + return 0;
>> +}
>> +EXPORT_SYMBOL(drm_sched_job_prealloc_dependency_slots);
>> +
>> /**
>> * drm_sched_job_add_dependency - adds the fence as a job dependency
>> * @job: scheduler job to add the dependencies to
>> @@ -878,10 +911,15 @@ int drm_sched_job_add_dependency(struct drm_sched_job
>> *job,
>> * engines involved, rather than the number of BOs.
>> */
>> xa_for_each(&job->dependencies, index, entry) {
>> - if (entry->context != fence->context)
>> + if (xa_is_zero(entry)) {
>
> If xa_for_each shows them I think we also need to skip them in
> drm_sched_job_dependency() and drm_sched_job_cleanup().
Oh, really good point. I've completely forgotten about them.
> Or remove the unused ones at arm time. Hm, we could also put a noisy fail if
> add_dependency allocates after a job is armed. (I can imagine a few unit
> tests for this once we merge them.)
Good point as well. I was also waiting for your unit testing stuff to land in
drm-misc-next so I can write a test for that.
Thanks,
Christian.
>
> Regards,
>
> Tvrtko
>
>> + /*
>> + * Reserved entries must not alloc memory, but let's
>> + * use GFP_ATOMIC just to be on the defensive side.
>> + */
>> + xa_store(&job->dependencies, index, fence, GFP_ATOMIC);
>> + } else if (entry->context != fence->context) {
>> continue;
>> -
>> - if (dma_fence_is_later(fence, entry)) {
>> + } else if (dma_fence_is_later(fence, entry)) {
>> dma_fence_put(entry);
>> xa_store(&job->dependencies, index, fence, GFP_KERNEL);
>> } else {
>> diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
>> index 1a7e377d4cbb..916e820b27ff 100644
>> --- a/include/drm/gpu_scheduler.h
>> +++ b/include/drm/gpu_scheduler.h
>> @@ -632,6 +632,8 @@ int drm_sched_job_init(struct drm_sched_job *job,
>> u32 credits, void *owner);
>> void drm_sched_job_arm(struct drm_sched_job *job);
>> void drm_sched_entity_push_job(struct drm_sched_job *sched_job);
>> +int drm_sched_job_prealloc_dependency_slots(struct drm_sched_job *job,
>> + unsigned int num_deps);
>> int drm_sched_job_add_dependency(struct drm_sched_job *job,
>> struct dma_fence *fence);
>> int drm_sched_job_add_syncobj_dependency(struct drm_sched_job *job,
>
